In a variety of technical fields, there is a need to determine the position of a first movable component of a device relative to a second component that is, for the most part, stationary. Thus, in a pipeline system with valves for example, it is of interest to determine the position of a valve body of a valve relative to the valve housing thereof, for example, in order to determine whether the valve is open or closed, or in order to determine how wide the valve is open. Likewise, it is also of interest to determine the position of a piston in a cylinder. There is frequently an interest to determine the absolute position of a first movable component relative to a second component, which is stationary for the most part, in reference to a fixed coordinate system of the second component. It is also frequently of interest to determine when the first movable component passes a specific position.
A device is known from the document DE 32 44 891 C2, in which several magnetically sensitive sensors are disposed along a measurement path. The output signals of the sensors are supplied to a multiplexer. The output of the multiplexer is supplied to evaluation electronics that from the multiplexer output signal generate a signal, and from this signal the position of a magnetic field-generating element relative to the sensors can be determined.
The document EP 1 209 439 B1 describes, in addition to a design comparable to DE 32 44 891 C2, an evaluation method that can evaluate the output signal of the multiplexer.
In industrial automation, it is standard to determine the piston position in pneumatic compressed air cylinders using magnetic sensors. In addition to microwaves, differential transformers (LVDT) and inductive sensor solutions (EP 0 693 673 A2), silicon-based magnetic sensors such as Hall sensors (EP 1 264 159 B1) and magnetoresistive sensors (DE 32 44 891 C2) are predominantly used as displacement transducers. Depending on the task, these devices are present as individual sensors for determining a switch point, or as an array of sensors for determining multiple switch points or absolute positions.
For this purpose, the piston is supplied with a position sensor. Typically, this is an annular magnet, the outer diameter of which corresponds approximately to the maximum diameter of the piston. Or this can be a substantially smaller disc magnet integrated at a location in the piston which is alongside a specific outer groove in the cylinder. The smaller, or respectively weaker, the magnets that are used, the smaller the danger of contamination due to magnetic chips on the one hand; on the other hand, magnetic interference fields gain greater influence on the measurement accuracy. The various types of the cylinders typically use different position sensors.
In the simplest case, when a magnet passes a displacement transducer, a sensor signal is generated that generates a switching signal with a predefined reference value in downstream electronics. Frequently it is desirable to subdivide the automated procedure into several steps, corresponding to which several switching points are required. In order to reduce the assembly complexity, it is not desirable to assemble several sensor switches for each switching point, but rather to have the displacement transducer perform this task. The measurement of an absolute position of the piston is even more advantageous. The corresponding switching points are then mapped in a downstream stored program control.
With the use of magnetoresistive sensors, which utilize the anisotropic magnetoresistance affect (AMR), it must be noted that with external fields that are too weak, as can occur with a remote element position, a reversal of magnetization procedures can occur in the active meanders, which leads to undefined sensor signals. For this reason, the document EP 0 783 666 B1 discusses a magnet which generates a magnetic field of sufficient strength in order to saturate the magnetoresistive material.
Based on this background, the problem addressed by the invention is to provide a device for generating a sensor signal and a method for determining the position of a magnetic field-generating element relative to a device for generating a sensor signal, with which the position of a magnetic field-generating element relative to a device can be better determined.